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I just got a new Lenovo Laptop which has been installed with Windows 7 and is supposed to have 250 GB hard disk.

Windows 7 reports that the hard disk drive has two parts: 221 GB C: and 9.76 GB Lenovo Recovery. The sum of the two parts is 230.76 GB.

If I remember correctly, if divide 250 GB by 1024 three times, I will get 232.8 GB, which should be what the OS reports as the hard drive size. But why the sum 230.76 GB of the two parts of hard drive is still smaller than 232.8 GB?

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  • For anyone that lands here, please read the question more carefully than the people who posted answers below. First of all, Tim had already accounted for binary/decimal units, so it’s not a matter of 1,000 vs. 1,024. Second, he was not asking about the free space on the drive being too low, he was asking about the total space, so it has nothing to do with file-system overhead.
    – Synetech
    Nov 24, 2013 at 21:31

6 Answers 6

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Because NTFS by design uses a piece of your volume for a MFT (Master File Table) which holds file names, creation dates, access permissions, and contents as metadata. The bigger the volume, the bigger the chunk NTFS will need.

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  • Do you also mean the whole C: disk size does not include the size for MFT? Is there some place under Windows reporting the size of the whole hard drive?
    – Tim
    Nov 18, 2009 at 4:58
  • 4
    No, the size does include the MFT. Think about it the MFT can grow so it the size didn't include the MFT you would see the size of the drive drop. Also in Disk Management if you switch the format from NTFS to FAT the size of the partition doesn't change.
    – shf301
    Nov 18, 2009 at 6:18
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    @shf you are very misinformed, and very downvote happy. First of all, the MFT size is defined by the size of your drive, and it is made once. This space allocated does not change in size, it preallocates enough up front for future changes. Also once you changed to FAT32, try a reboot?
    – John T
    Nov 18, 2009 at 6:50
  • 4
    Maybe you are thinking of the MFT zone which NTFS reserves, but that is not the size of the MFT itself and that zone can be used to store files if the rest of the drive is filled. See technet.microsoft.com/en-us/library/cc781134%28WS.10%29.aspx
    – shf301
    Nov 19, 2009 at 5:20
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    shf301 is correct; the MFT does grow and is not defined only by the size of the volume. Go ahead and do an experiment if you want. Create a small NTFS volume, then create 1,000,000 little files on it. You will see the MFT grow because it needs more space to store the information for all those files. The size of the volume does indeed include the MFT, it is simply the size of the volume and $MFT is nothing more than a file in that volume, so its size is included.
    – Synetech
    Nov 24, 2013 at 21:24
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Actually. This is because harddrive manufacturers conform to the 1MB = 1,000 KB rule and your OS uses the 1MB = 1,024 KB rule.

This would probably account for most of your lost space. Its normal. You will NEVER buy a drive that is the size it specifies, ever. I looked in to it myself not too long ago :)

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  • Ah, you mentioned something like that also. Ah well, good clarification for everyone else! :D Also, NTFS holds additional space/information for each additional partition used, so you will probably never see 100% of your space within Windows.
    – SevenT2
    Nov 18, 2009 at 5:33
  • All the drives you buy are the size they specify. Your software is just reporting the size wrong.
    – endolith
    Jun 15, 2011 at 4:59
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    Re-read the question (even the original); he already accounted for that.
    – Synetech
    Nov 24, 2013 at 21:25
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Unfortunately, life's hard and this is one of those things that annoys people non stop.

At least you are smart and understand that there is a conversion that needs to be made.

The "extra" space is usually used up by the allocation table, meta data and various other items that just make it work without you needing to think of it... it is nothing to worry about.

If you want to make 100% sure you have the correct drive, go in to device manager and expand hard drives, find the model number and Google it. If it reports the correct drive (which it should) there shouldn't be anything to worry about.

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  • He’s not asking about free space, he’s talking about total space. The total size of the volume is not affected by file-system structures, only the free space would be. The total volume size includes the MFT and other NTFS special files.
    – Synetech
    Nov 24, 2013 at 21:28
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A chunk of your loss at least is due to the partition table eating it's entire track--a horribly inefficient legacy we are left with.

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  • Um, what‽ Partitions tables are only a few clusters; there’s no way partition tables would take up 2GB!
    – Synetech
    Nov 24, 2013 at 21:26
  • Except they eat one track as the next partition needs to start on the next track. I do agree it's not 2gb, though. Nov 24, 2013 at 23:28
  • Yes, that was one of the things that always annoyed me whenever I tried to size my partitions accurately; the partition programs would always round. But no, it’s indeed not 2GB, it’s ~7MB, plus, the excess doesn’t just disappear, it gets added to the previous/next partition.
    – Synetech
    Nov 24, 2013 at 23:41
  • @Synetech It depends on the capacity of a track. I really doubt a 4tb drive has 7mb tracks. Nov 24, 2013 at 23:52
  • I don’t think that’s how it works; it doesn’t use up a whole track. You can check with a partition program; just use the resize function and observe how it rounds the partition size on different sized drives. Over the years, I have seen these programs round to the nearest ~7.5MB on drives of all sizes.
    – Synetech
    Nov 25, 2013 at 0:01
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It could just be the manufacturer rounding the hard drive size to the nearest whole gigabyte. If we start with what Windows shows and calculate what that work out to in billion bytes:

232.8 * 2^30 / 10^9 = 249.9671 million bytes

So they just rounded the marketing size to 250, cause whose going to miss 0.0329 million bytes.

If you can get the module number of the hard drive and get it's detailed specs and find it's sector count you can determine what the actual capacity of the drive really is.

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A part of the issue with advertised harddrive space and actual harddrive space is down to the fact that harddrives in shops are advertised with storage information in Decimal (Base 10) as opposed to how computers understand storage, which is in Binary (Base 2).

What is the difference?

Well, let's look at binary figures compared to decimal. These become apparent when you indicate the base figure (sub 2 for binary and sub 10 for decimal)

Binary

JEDEC, who sets the Global Standards for the Microelectronics Industry uses the binary definitions of Megabyte and Gigabyte which is exactly how computers generally would see things withinin programming etc. JEDEC states that:

A multiplier equal to 1024 (210).

A multiplier equal to 1 048 576 (220 or K2, where K = 1024).

As you can see, each step up (byte to kilobyte, kilobyte to megabyte...) is in multiples of 1024.

Decimal

Harddrives are sold in decimal storage figures and these are different.

In decimal:

  • 1KB (kilobyte) = 100010 bytes
  • 1MB (Megabyte) = 100010 kilobytes ... and so on

As you can see, each step up (byte to kilobyte, kilobyte to megabyte...) is in multiples of 100010.

IEEE/ASTM SI 10‑1997 states that the practice of stating that 1 Megabyte = 1024 kilobytes frequently leads to confusion and is to be deprecated. Further confusion results from the popular use of a "megabyte" consisting of 1 024 000 bytes to define the capacity of the familiar "1.44‑MB" floppy disk. An alternative system is found in Amendment 2 to IEC 60027‑2: Letter symbols to be used in electrical technology - Part 2, and the IEC states that figures represented in base 2 are to be referred to as kibibyte or mebibyte or gibibyte etc.

What is the problem?

In computing, within programming and when referring to data storage within semiconductors etc, everything is in Base 2. When you buy a 1TB harddrive you are buying a harddrive which is stated to have be 1012 bytes storage (1,000,000,000,000 bytes). This causes confusion to those who know about binary data and the true figures within computers and would expect to be buying 1,099,511,627,776 bytes and actually getting 91% of that space.

Where you are short changed is in the following:

Let's say all your files to be stored in that harddrive are exactly 1MB (Base 2) each in size. With 1TB spare:

You should be able to fit 1,048,576 files on a 1TB drive. But you can't.
You are actually only able to fit 953,674 files.

Things are also bad when you are storing digital videos. Let's say at 1GB (Base 2) each. With a 1TB (advertised space) harddrive:

You should be able to fit 1,024 files
You are actually only able to fit 931 files (90 files short)

So, as a quick reference to show the amount that the actual values differ compared to the advertised for each common referenced value:

  • Megabyte difference = 48,576 bytes (47KB)
  • Gigabyte difference = 73,741,824 bytes (72,013KB or 70MB)
  • Terabyte difference = 99,511,627,776 bytes (97,179,324KB or 94,901MB or 92GB)

A case in point is that a hard drive in my computer, advertised at 2TB in size, is actually 1863GB in size according to my computer instead of 2048GB. That is 185GB short (92.5GB per advertised Terabyte).

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  • Please do not post the same answer to multiple questions. If the same information really answers both questions, then one question (usually the newer one) should be closed as a duplicate of the other. You can indicate this by voting to close it as a duplicate or, if you don't have enough reputation for that, raise a flag to indicate that it's a duplicate. Otherwise tailor your answer to this question and don't just paste the same answer in multiple places.
    – DavidPostill
    Sep 14, 2020 at 16:56
  • Thanks for that @DavidPostill. The duplicate answer is deleted and I have put a couple of duplicates (including this one) in the comments of the other question. Sep 14, 2020 at 17:24

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